Sem scanner sensing apparatus, system and methodology for early detection of ulcers

ABSTRACT

A handheld, conforming capacitive sensing apparatus configured to measure Sub-Epidermal Moisture (SEM) as a mean to detect and monitor the formation of pressure ulcers. The device incorporates an array of electrodes which are excited to measure and scan SEM in a programmable and multiplexed manner by a battery-less RF-powered chip. The scanning operation is initiated by an interrogator which excites a coil embedded in the apparatus and provides the needed energy burst to support the scanning/reading operation. Each electrode measures the equivalent sub-epidermal capacitance corresponding and representing the moisture content.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/668,047 filed on Nov. 2, 2012, incorporated herein by reference inits entirety, which is a 35 U.S.C. §111(a) continuation of PCTinternational application number PCT/US2011/035618 filed on May 6, 2011,incorporated herein by reference in its entirety, which claims thebenefit of U.S. provisional patent application Ser. No. 61/332,755 filedon May 8, 2010, incorporated herein by reference in its entirety, andwhich claims the benefit of U.S. provisional patent application Ser. No.61/453,852 filed on Mar. 17, 2011, incorporated herein by reference inits entirety. Priority is claimed to each of the foregoing applications.

The above-referenced PCT international application was published as PCTInternational Publication No. WO 2011/143071 on Nov. 17, 2011 andrepublished on Apr. 5, 2012, and is incorporated herein by reference inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF COMPUTER PROGRAM APPENDIX

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document is subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. §1.14.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains generally to monitoring skin pressure ulcers andmore particularly to skin ulcer monitoring via measurement ofSub-epidermal Moisture (SEM).

2. Description of Related Art

Patients' skin integrity has long been an issue of concern for nursesand in nursing homes. Maintenance of skin integrity has been identifiedby the American Nurses Association as an important indicator of qualitynursing care. Meanwhile, pressure ulcers remain a major health problemparticularly for hospitalized older adults. When age is considered alongwith other risk factors, the incidence of pressure ulcers issignificantly increased. Overall incidence of pressure ulcers forhospitalized patients ranges from 2.7% to 29.5%, and rates of greaterthan 50% have been reported for patients in intensive care settings. Ina multicenter cohort retrospective study of 1,803 older adultsdischarged from acute care hospitals with selected diagnoses, 13.2%(i.e., 164 patients) demonstrated an incidence of stage I ulcers. Ofthose 164 patients, 38 (16%) had ulcers that progressed to a moreadvanced stage. Pressure ulcers additionally have been associated withan increased risk of death one year after hospital discharge. Theestimated cost of treating pressure ulcers ranges from $5,000 to $40,000for each ulcer, depending on severity.

Therefore, there is an urgent need to develop a preventive solution tomeasure moisture content of the skin as a mean to detect early symptomsof ulcer development.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present invention is a smart compact capacitive sensingconforming handheld apparatus configured to measure Sub-epidermalMoisture (SEM) as a mean to detect and monitor the development ofpressure ulcers. The device incorporates an array of electrodes whichare excited to measure and scan SEM in a programmable and multiplexedmanner by a battery-less RF-powered chip. The scanning operation isinitiated by an interrogator which excites a coil embedded in theapparatus and provides the needed energy burst to support thescanning/reading operation. Each embedded electrode measures theequivalent sub-epidermal capacitance corresponding and representing themoisture content of the target surface.

An aspect of this invention is the in situ sensing and monitoring ofskin or wound or ulcer development status using a wireless,biocompatible RF powered capacitive sensing system referred to as smartSEM imager. The present invention enables the realization of smartpreventive measures by enabling early detection of ulcer formation orinflammatory pressure which would otherwise have not been detected foran extended period with increased risk of infection and higher stageulcer development.

In one beneficial embodiment, the handheld capacitive sensing imagerapparatus incorporates pressure sensing components in conjunction withthe sensing electrodes to monitor the level of applied pressure on eachelectrode in order to guarantee precise wound or skin electricalcapacitance measurements to characterize moisture content. In summary,such embodiment would enable new capabilities including but not limitedto: 1) measurement capabilities such as SEM imaging and SEM depthimaging determined by electrode geometry and dielectrics, and 2) signalprocessing and pattern recognition having automatic and assuredregistration exploiting pressure imaging and automatic assurance ofusage exploiting software systems providing usage tracking.

One major implication of this sensor-enhanced paradigm is the ability tobetter manage each individual patient resulting in a timelier and moreefficient practice in hospitals and even nursing homes. This isapplicable to patients with a history of chronic wounds, diabetic footulcers, pressure ulcers or post-operative wounds. In addition,alterations in signal content may be integrated with the activity levelof the patient, the position of patient's body and standardizedassessments of symptoms. By maintaining the data collected in thesepatients in a signal database, pattern classification, search, andpattern matching algorithms can be developed to better map symptoms withalterations in skin characteristics and ulcer development. This approachis not limited to the specific condition of ulcer or wound, but may havebroad application in all forms of wound management and even skindiseases or treatments.

One aspect is apparatus for sensing sub-epidermal moisture (SEM) from alocation external to a patient's skin. The apparatus includes a bipolarRF sensor embedded on a flexible substrate, and a conformal pressure paddisposed adjacent and underneath the substrate, wherein the conformalpressure pad is configured to support the flexible substrate whileallowing the flexible substrate to conform to a non-planar sensingsurface of the patient's skin. The apparatus further includes interfaceelectronics coupled to the sensor; wherein the interface electronics areconfigured to control emission and reception of RF energy to interrogatethe patient's skin.

Another aspect is a method for monitoring the formation of pressureulcers at a target location of a patient's skin. The method includes thesteps of positioning a flexible substrate adjacent the target locationof the patient's skin; the flexible substrate comprising one or morebipolar RF sensors; conforming the flexible substrate to the patient'sskin at the target location; exciting the one or more bipolar RF sensorto emit RF energy into the patient's skin; and measuring the capacitanceof the skin at the target location as an indicator of the Sub-EpidermalMoisture (SEM) at the target location.

Further aspects of the invention will be brought out in the followingportions of the specification, wherein the detailed description is forthe purpose of fully disclosing preferred embodiments of the inventionwithout placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 illustrates an assembled perspective component view of the SEMScanner of the present invention.

FIG. 2 illustrates a perspective view of a Kapton-based conformingsensing substrate assembly of the present invention.

FIG. 3 shows a top view of an exemplary concentric sensing electrode inaccordance with the present invention.

FIG. 4 illustrates a side view of a flex stack-up for the Kapton-basedconforming sensing substrate shown in FIG. 2.

FIG. 5 illustrates a side view of an alternative flex stack-up for aKapton-based conforming sensing substrate.

FIG. 6 shows a top view of two-electrode sensing Kapton-based flexsensor substrates for three alternative types of capacitive sensingconcentric electrodes.

FIG. 7 illustrates an exploded perspective component view of the SEMscanner of FIG. 1.

FIG. 8 illustrates a schematic side view of the SEM scanner of FIG. 1.

FIG. 9 illustrates a schematic side view of the SEM scanner of FIG. 8 incontact with subject skin.

FIG. 10 illustrates a perspective view of an assembled SEM scanner withan alternative array of sensors in accordance with the presentinvention.

FIG. 11 is a plot of normalized responses of the tested electrodes ofthe present invention.

FIG. 12 is a graph of measured equivalent capacitance for dry volar armfor three different concentric sensor electrodes.

FIG. 13 is a plot of time dependent fractional change in capacitancerelative to dry skin for three different concentric sensor electrodes(after 30 minutes of applying lotion).

FIG. 14 is a plot of time dependent fractional change in capacitancerelative to dry skin for three different concentric sensor electrodes(after 15 minutes of applying lotion).

FIG. 15 is a plot of fractional change vs. time.

FIG. 16 shows a SEM scanner electrode system and electrode layeringproviding proper shielding from interference.

FIG. 17 shows an SEM scanner mechanical compliance for electrodesdeveloped to enable probing of bony prominence.

DETAILED DESCRIPTION OF THE INVENTION

In one exemplary embodiment, a smart handheld capacitive sensing deviceaccording to the present invention employs a programmable sensingelectrode array. This is based on methods that use an interrogator toexcite the embedded electrodes.

FIG. 1 illustrates an SEM scanning/sensing apparatus 10 according to thepresent invention. The scanner 10 comprises five main components,including a top silicone edge sealing gasket 18 encircling aKapton-based sensing substrate 16, which rests on a conformal siliconepressure pad 12. A thick annular silicone spacer 20 is disposed underpressure pad to provide free space for the pressure pad to deform. Thebottom layer comprises an interface electronics package enclosure 22that houses interface circuitry for interrogating and transmitting datafor evaluation. These five main components are described in furtherdetail below.

In the embodiment shown in FIG. 1, an array 14 of individual RFelectrode sensors 24 and 26 is embedded on a flexible biocompatiblesubstrate 16. Substrate 16 may comprise a laminated Kapton (Polyimide)chip-on-flex.

FIG. 2 illustrates one embodiment of a Kapton sensor substrate 16 a thatcomprises an array 14 of differing sized concentric sensing electrodes.A flexible biocompatible Polyimide or Kapton substrate 32 comprises alayer of sensing pads 14 and 15 coated on one side with an ultra thincover layer 30 of Polyimide (e.g. CA335) to isolate pads electrodes14,15 from direct moisture contact and also to provide a uniform contactsurface.

In FIG. 2, sample capacitive sensing electrodes 14 are shown indifferent sizes (e.g. 24, 26, and 29), which are manipulated to achieveand sense different depths of skin. Sensing electrodes 14 may compriseany number of different shape and configurations, such as the concentriccircles of array 14, or the interdigitating fingers of sensor 15.

FIG. 3 illustrates a close-up top view of a concentric sensing pad 26 inaccordance with the present invention. Pad 26 comprises a bipolarconfiguration having a first electrode 36 comprising an outer annularring disposed around a second inner circular electrode 38. Outer ringelectrode 36 has an outer diameter D_(o) and an inner diameter D_(i)that is larger than the diameter D_(c) of the circular inner electrode38 to form annular gap 40. Inner circular electrode 38 and outer ringelectrode 36 are coupled electrically to interface electronics in theinterface electronics package 22. As shown in greater detail in FIGS. 4and 5, electrodes 36 and 38 are disposed on separate layers within thesubstrate assembly 16.

The dimensions of the sensor pads 24, 26 generally correspond to thedepth of interrogation into the derma of the patient. Accordingly, alarger diameter pad (e.g. pad 26 or 29) will penetrate deeper into theskin than a smaller pad. The desired depth may vary depending on theregion of the body being scanned, or the age, skin anatomy or othercharacteristic of the patient. Thus, SEM scanner 10 may comprise anarray of different sized pads (e.g. small pads 24 and medium sized pads26 shown in FIG. 1) each individually coupled to the interfaceelectronics package 22.

FIG. 4 illustrates side view of a flex stack-up for a Kapton basedsubstrate assembly 16, where thin adhesive layers 42 are used to attacha Kapton layer 32 in between copper layers 44 and 46, all of which aredisposed between upper coverlay 30 and lower coverlay 48. A stiffener 50is disposed under lower coverlay 48, being positioned directly undercopper layer 46 of the sensing pads. The stiffener 50 forms a rigidportion of the substrate where sensing pad array 14, connectors (e.g.connectors 66, 76, or 86 shown in FIG. 6) and interfacing (e.g. leadwires 34) are located, so that these areas do not deform, whereas therest of the substrate is free to deform. The top copper layer 44 is usedto etch out electrode array 14 and corresponding copper routing 34 tothe connectors. The bottom copper layer 46 preferably comprises acrisscross ground plane to shield electrode array 14 from unwantedelectromagnetic interference.

In one embodiment, the flex substrate 16 assembly comprises Pyralux FRmaterial from Dupont. In an exemplary configuration, approximately 5 milthick FR9150R double-sided Pyralux FR copper clad laminate is used asthe Kapton substrate. Top coverlay 30 comprises Pyralux 5 mil FR0150 andthe bottom coverlay 48 comprises 1 mil FR0110 Pyralux. The thickness ofthe top FR0150 coverlay 30 is an important parameter as it affects thesensitivity of sensing electrodes in measuring skin moisture content.Copper layers 44, 46 are generally 1.4 mil thick, while adhesive layers42 are generally 1 mil thick. The stiffener 50 is shown in FIG. 4 isapproximately 31 mil thick.

FIG. 5 shows a side view of a preferred alternative flex stack-up for aKapton based substrate 120, where thin adhesive layers 42 (1 mil) areused to attach an 18 mil Kapton layer 122 in between 1.4 mil copperlayers 44 and 46, all of which are disposed between 2 mil upper coverlay30 and 1 mil lower coverlay 48. A stiffener 50 is disposed under lowercoverlay 48, being positioned directly under copper layer 46 of thesensing pad. The 31 mil FR4 stiffener 126 forms a rigid portion of thesubstrate under the array 14 of sensing pads, connectors 66 andinterfacing 34. A 2 mil layer of PSA adhesive 124 is used between thebottom coverlay 48 and stiffener 126. The layering of assembly 120 isconfigured to provide proper shielding from interference.

FIG. 6 shows a top view of three separate and adjacently arrangedconcentric bipolar electrode sensing Kapton-based flex pads 60, 70 and80 having different sized capacitive sensing concentric electrodes. Pad60 comprises a substrate having two large concentric electrodes 62 wiredthrough substrate 64 via connectors 34 to lead line inputs 66. Pad 70comprises a substrate having two medium concentric electrodes 72 wiredthrough substrate 74 to lead line inputs 76. Pad 80 comprises asubstrate having two small concentric electrodes 82 wired throughsubstrate 84 to lead line inputs 86. The configuration shown in FIG. 6is optimized for cutting/manufacturing and also to avoid interferencebetween data lines and sensors. Each of the bipolar electrode pads isindividually wired to the electronics package 22 to allow forindependent interrogation, excitation, and data retrieval.

FIG. 7 illustrates an exploded perspective component view of the SEMscanner 10. The silicone edge sealing gasket 18 is applied over theKapton sensor substrate assembly 16 to seal and shield the edgeinterface connectors through which interface electronics package 22excite and controls the sensing electrode array 14. The Kapton sensorsubstrate assembly 16 rests on a conformal silicone pressure pad 12 thatprovides both support and conformity to enable measurements over bodycurvature and bony prominences.

In one beneficial embodiment, pressure sensor 11 may be embedded undereach sensing electrode 24, 26 (e.g. in an identical array not shown),sandwiched between Kapton sensor substrate 26 and the conformal siliconepressure pad 28 to measure applied pressure at each electrode, thusensuring a uniform pressure and precise capacitance sensing.

Lead access apertures 28 provide passage for routing the connector wires(not shown) from the substrate connectors (e.g. 66, 76, 86) through thepressure pad 12, annular spacer 20 to the interface electronics 22.

The annular silicone spacer 20 comprises a central opening 27 thatprovides needed spacing between the conformal silicone pressure pad 12and the interface electronics package 22 to allow the pressure pad 12and flexible substrate to conform in a non-planar fashion to conductmeasurements over body curvatures or bony prominences.

In one embodiment, the interface electronics package 22 is connected toa logging unit or other electronics (not shown) through wire-line USBconnector 56.

The interface electronics package 22 preferably comprises an enclosurethat contains all the electronics (not shown) needed to excite, programand control the sensing operation and manage the logged data. Theelectronics package 22 may also comprise Bluetooth or other wirelesscommunication capabilities to allow for transfer of sensing data to acomputer or other remote device. Docked data transfer is alsocontemplated, in addition to real-time Bluetooth transfer. A gatewaydevice (not shown) may be used for communicating with the SEM device 10and data formatting prior to upload to a computer or backend server.

FIG. 8 is a schematic side view of the SEM scanner 10 in the nominalconfiguration, showing the edge gasket 18 over Kapton substrate 16, andlead access apertures 28, which provide access through annular spacer 20and conformal pad 12 to electronics 22.

FIG. 9 illustrates a schematic side view of the SEM scanner 10 incontact with the target subject 25. The annular silicone spacer 20provides enough spacing for conforming silicone pad 12 to conform to thetarget surface 25. The conforming silicone pad 12 enables continuouscontact between the substrate 16 and patient's skin 25, thus minimizinggaps between the substrate 16 and patient's skin 25 that could otherwiseresult in improper readings of the patient anatomy. Electrode array 14,which is embedded in substrate 16, is shown interrogating into the dermaof tissue 25 by directing emission of an RF signal or energy into theskin and receiving the signal and correspondingly reading the reflectedsignal. The interrogator or electronics package 22 excites electrodecoil 14 by providing the needed energy burst to support thescanning/reading of the tissue. Each embedded electrode 14 measures theequivalent sub-epidermal capacitance corresponding to the moisturecontent of the target skin 25.

While other energy modalities are contemplated (e.g. ultrasound,microwave, etc.), RF is generally preferred for its resolution in SEMscanning.

FIG. 10 illustrates a perspective view of an assembled SEM scanner 10with an alternative substrate 16 b having an array 14 of ten sensorsdispersed within the substrate 16 b. This larger array 14 provides for alarger scanning area of the subject anatomy, thus providing a completepicture of the target anatomy in one image without having to generate ascanning motion. It is appreciated that array 14 may comprise any numberof individual sensors, in be disposed in a variety of patterns.

The SEM scanner 10 was evaluated using a number of different sized andtypes of sensors 26. Table 1 illustrates electrode geometries are usedthroughout the following measurements. As shown in FIG. 1 the outer ringelectrode diameter D_(o) varied from 5 mm for the XXS pad, to 55 mm forthe large pad. The outer ring electrode inner diameter D_(i) varied from4 mm for the XXS pad, to 40 mm for the large pad. The inner electrodediameter D_(c) varied from 2 mm for the XXS pad, to 7 mm for the largepad. It is appreciated that the actual dimensions of the electrodes mayvary from ranges shown in these experiments. For example, the contactdiameter may range from 5 mm to 30 mm, and preferably ranges from 10 mmto 20 mm.

To measure the properties of each sensor size listed in Table 1, thesensors were fabricated using both Kapton and rigid board. In testingwith the rigid sensor pads, lotion was applied to the thumb continuouslyfor 15 minutes.

FIG. 11 is a plot of normalized responses of the tested electrodes ofthe present invention. The four sensors' (XXS, XS, S, M) normalizedresponses are compared in FIG. 11 and Table 2.

As can be seen in FIG. 11 and Table 2, the S electrode appears to bemost responsive overall to the presence of moisture. Both the M and Selectrodes seem to exhibit a peak. This suggests a depth dependency ofthe moisture being absorbed into the skin, as the roll-off from the Melectrode occurs about 5 minutes after the peak for S electrode.

The SEM scanner 10 was also tested on the inner arm. A resistivepressure sensor (e.g. sensor 11 shown in FIG. 7) was also used tomeasure pressure applied on sensor to the arm. This way, constantpressure is applied across measurements. First, the dry inner arm wasmeasured using the XS, S and M electrodes. Then, the same area wasmasked off with tape, and moisturizer lotion was applied for 30 minutes.Subsequent measurements were made on the same location after cleaningthe surface.

FIG. 12 is a graph of measured equivalent capacitance for dry Volar armfor three different sized (M, S, XS) concentric sensor electrodes beforeapplying the commercial lotion moisturizer.

FIG. 13 is a plot of time dependent fractional change in capacitancerelative to dry skin for three different concentric sensor electrodes(after 30 minutes of applying lotion).

FIG. 14 is a plot of time dependent fractional change in capacitancerelative to dry skin for three different concentric sensor electrodes(after 15 minutes of applying lotion) on two subjects. This experimentwas performed with faster sampling intervals and with lotion applied for15 minutes only on forearms of two test subjects. Again, a resistivepressure sensor was used to measure pressure applied on sensor to thearm. This way, constant pressure is applied across measurements. Firstthe dry inner arm was measured using the XS, S and M electrodes. Thenthe same area was masked off with tape, and lotion was applied for 15minutes. Subsequent measurements were made on the same location every 5minutes. Pressure was maintained at 50 k Ohms, and the forearm wastested again. We noticed an interesting observation for the case “F” incomparison to case “A” and also compared to previous measurements. Case“F” took a shower right before running the measurements and hence as aresult his skin was relatively saturated with moisture. As a result, weobserved less degree of sensitivity to the applied deep moisturizer forcase “F”.

The experiment was performed again for case “F”, with a time resolutionof 3 minutes, knowing that the subject did not shower in the morningbefore the test. The lotion was applied to the inner forearm for 15minutes. Pressure was maintained at 50 k Ohms. The results confirm thesensitivity of the measurement to the residual skin moisture.

FIG. 15 is a plot of results for fractional change vs. time for M, S andXS electrodes.

FIG. 16 shows a preferred embodiment of a layered SEM scanner electrodesystem 100 having a first electrode pad 102 and second electrode pad104. Pad 104 is connected to lead line inputs 116 via wiring 34 alongcurved path 112. Pad 102 is connected to lead line inputs 110 via wiring34 along curved path 106. A stiffener layer (e.g. layer 126 in FIG. 5)is provided directly under lead inputs 110 and 116 (see footprint 108and 114 respectively) and under pads 102 and 104 (see footprint 122 and120 respectively).

In this embodiment, the electrode size is approximately 2300 in width by3910 mil in height.

FIG. 17 illustrates the SEM Scanner mechanical compliance(force-displacement relationship) for electrodes of system 100,developed to enable probing of bony prominence. The diamond symbols showthe upper electrode 104 response, square symbols show the lowerelectrode 102 response.

The SEM scanner device 10 may also include other instruments, such as acamera (not shown), which can be used to take pictures of the wound, ordevelop a scanning system to scan barcodes as a login mechanism or aninterrogator.

Patients using the SEM scanner device 10 may wear a bracelet (not shown)that contains data relating to their patient ID. This ID can be scannedby the camera embedded in the SEM scanner 10 to confirm correct patientID correspondence. Alternatively, a separate RF scanner (not shown) maybe used for interrogating the bracelet (in addition to the camera).

The SEM scanner device 10 is preferably ergonomically shaped toencourage correct placement of the device on desired body location.

The SEM Scanner device 10 of the present invention is capable ofgenerating physical, absolute measurement values, and can producemeasurements at multiple depths.

From the foregoing it will be appreciated that the present invention canbe embodied in various ways, which include but are not limited to thefollowing:

1. An apparatus for sensing sub-epidermal moisture from a locationexternal to a patient's skin, comprising: a bipolar RF sensor embeddedon a flexible substrate; a conformal pressure pad disposed adjacent andunderneath the substrate; wherein the conformal pressure pad isconfigured to support the flexible substrate while allowing the flexiblesubstrate to conform to a non-planar sensing surface of the patient'sskin; and interface electronics coupled to the sensor; wherein saidinterface electronics is configured to control emission and reception ofRF energy to interrogate the patient's skin.

2. The apparatus of embodiment 1, further comprising: an annular spaceradjacent and underneath the conformal pressure pad; wherein the annularspacer comprises a central opening configured to allow the conformalpressure pad to deflect freely into the central opening.

3. The apparatus of embodiment 1, further comprising: an array ofbipolar RF sensors spaced across the flexible substrate; wherein each ofthe sensors is independently coupled to the interface electronics toindependently interrogate the patient's skin.

4. The apparatus of embodiment 3: wherein each of the sensors isconfigured to measure an equivalent sub-epidermal capacitance of atarget region of skin; said sub-epidermal capacitance corresponding tothe moisture content of the target region of skin.

5. The apparatus of embodiment 4: wherein the array of sensors comprisesa first sensor having a first contact area and a second sensor having asecond contact area larger than the first sensor; wherein the first andsecond sensors interrogate the skin at different depths.

6. The apparatus of embodiment 4: wherein the substrate comprises asubstrate assembly comprising a substrate layer; and wherein the sensorcomprises a sensing pad having a first electrode embedded on a firstside of the substrate and a second electrode embedded on a second sideof the substrate.

7. The apparatus of embodiment 6, further comprising a biocompatiblecover layer disposed over said first side of said substrate layer.

8. The apparatus of embodiment 6, further comprising a cover layerdisposed under said second side of said substrate layer.

9. The apparatus of embodiment 6, further comprising a stiffener layerdisposed under said second side of said substrate layer; wherein thestiffener layer comprises a footprint substantially similar to that ofthe sensor array.

10. The apparatus of embodiment 6: wherein said first electrodecomprises an annular ring having an inner radius and an outer radius;wherein said second electrode comprises an outer radius having a smallerdiameter than the inner radius of the first electrode; and wherein saidsecond electrode is concentric with said first radius.

11. The apparatus of embodiment 1, wherein the interface electronics areconfigured to transmit data retrieved from said sensors.

12. The apparatus of embodiment 4, further comprising: a pressure sensorpositioned in line with said RF sensor; said pressure sensor configuredto measure an applied pressure of the substrate at a location on thepatient's skin.

13. The apparatus of embodiment 1, wherein the flexible substratecomprises Kapton or Polyimide.

14. A scanner for sensing sub-epidermal moisture from a locationexternal to a patient's skin, comprising: an array of bipolar RF sensorsembedded on a flexible substrate; and a conformal pressure pad disposedadjacent and underneath the substrate; wherein the conformal pressurepad is configured to support the flexible substrate while allowing theflexible substrate to conform to a non-planar sensing surface of thepatient's skin; wherein said sensor array is configured to emit andreceive RF energy to interrogate the patient's skin; and wherein each ofthe sensors are independently are individually wired to independentlyinterrogate the patient's skin.

15. The scanner of embodiment 14, further comprising: interfaceelectronics coupled to the sensor; wherein said interface electronics isconfigured to control the emission and reception of RF energy.

16. The scanner of embodiment 14, further comprising: an annular spaceradjacent and underneath the conformal pressure pad; wherein the annularspacer comprises a central opening configured to allow the conformalpressure pad to deflect freely into the central opening.

17. The scanner of embodiment 14: wherein each of the sensors isconfigured to measure an equivalent sub-epidermal capacitance of atarget region of skin; said sub-epidermal capacitance corresponding tothe moisture content of the target region of skin.

18. The scanner of embodiment 14: wherein the array of sensors comprisesa first sensor having a first contact area and a second sensor having asecond contact area larger than the first sensor; and wherein the firstand second sensors interrogate the skin at different depths.

19. The scanner of embodiment 14: wherein each sensor comprises a firstelectrode in the form of an annular ring having an inner radius and anouter radius and a second electrode comprising an outer radius having asmaller diameter than the first electrode; and wherein said secondelectrode is concentric with said first radius.

20. The scanner of embodiment 19: wherein the substrate comprises asubstrate assembly comprising a substrate layer; and wherein the firstelectrode is embedded on a first side of the substrate and the secondelectrode embedded on a second side of the substrate.

21. The scanner of embodiment 20, further comprising: an upperbiocompatible cover layer disposed over said first side of saidsubstrate layer and a lower cover layer disposed under said second sideof said substrate layer.

22. The scanner of embodiment 20, further comprising: a stiffener layerdisposed under said second side of said substrate layer; wherein thestiffener layer comprises a footprint substantially similar to that ofthe sensor array.

23. The scanner of embodiment 14, further comprising: an array ofpressure sensors positioned in line with said RF sensor; said pressuresensors are configured to measure an applied pressure of the substrateat corresponding locations on the patient's skin.

24. A method for monitoring the formation of pressure ulcers at a targetlocation of a patient's skin, comprising: positioning a flexiblesubstrate adjacent the target location of the patient's skin; theflexible substrate comprising one or more bipolar RF sensors; conformingthe flexible substrate to the patient's skin at the target location;exciting the one or more bipolar RF sensor to emit RF energy into thepatient's skin; and measuring the capacitance of the skin at the targetlocation as an indicator of the Sub-Epidermal Moisture (SEM) at thetarget location.

25. The method of embodiment 24: wherein the one or more sensorscomprise an array of sensors disposed across said substrate; and whereinthe one or more sensors are individually controlled to independentlyexcite the one or more sensors.

26. The method of embodiment 24, further comprising: measuring anapplied pressure of the substrate at the target location on thepatient's skin.

27. The method of embodiment 25, further comprising: measuring anapplied pressure of the substrate on the patient's skin at each of thesensors in the array.

Although the description above contains many details, these should notbe construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Therefore, it will be appreciated that the scope ofthe present invention fully encompasses other embodiments which maybecome obvious to those skilled in the art, and that the scope of thepresent invention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” All structural, chemical, and functionalequivalents to the elements of the above-described preferred embodimentthat are known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe present claims. Moreover, it is not necessary for a device or methodto address each and every problem sought to be solved by the presentinvention, for it to be encompassed by the present claims. Furthermore,no element, component, or method step in the present disclosure isintended to be dedicated to the public regardless of whether theelement, component, or method step is explicitly recited in the claims.No claim element herein is to be construed under the provisions of 35U.S.C. 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for.”

TABLE 1 Symbol XXS XS S M L Contact Diameter 5 10 20 23 55 (mm) ApproxOuter D_(o) (mm) 5 10 20 23 55 Approx Middle D_(i) (mm) 4 6 10 15 40Approx Inner D_(c) (mm) 2 2 4 5 7

TABLE 2 Tabulated Normalized Responses of M, S, XS and XXS ElectrodesTime M M Baseline S S Baseline XS XS Baseline XXS XXS Baseline 0 2.322.04 1.89 1.5 0.261 0.24 1.12 1.04 5 2.32 2.04 1.9 1.5 0.256 0.24 1.11.04 10 2.38 2.04 1.92 1.5 0.259 0.24 1.07 1.04 15 2.4 2.04 1.99 1.50.255 0.24 1.06 1.04 20 2.39 2.04 1.93 1.5 0.248 0.24 1.05 1.04 25 2.252.04 1.92 1.5 0.25 0.24 1.04 1.04 30 2.21 2.04 1.88 1.5 0.248 0.24 1.041.04 35 2.18 2.04 1.86 1.5 0.245 0.24 1.04 1.04

What is claimed is:
 1. An apparatus for sensing sub-epidermal moisturefrom a location external to a patient's skin, comprising: a bipolar RFsensor embedded on a flexible substrate; a conformal pressure paddisposed adjacent and underneath the substrate; wherein the conformalpressure pad is configured to support the flexible substrate whileallowing the flexible substrate to conform to a non-planar sensingsurface of the patient's skin; and interface electronics coupled to thesensor; wherein said interface electronics are configured to controlemission and reception of RF energy to interrogate the patient's skin.2. An apparatus as recited in claim 1, further comprising: an annularspacer adjacent and underneath the conformal pressure pad; wherein theannular spacer comprises a central opening configured to allow theconformal pressure pad to deflect freely into the central opening.
 3. Anapparatus as recited in claim 1, further comprising: an array of bipolarRF sensors spaced across the flexible substrate; wherein each of thesensors is independently coupled to the interface electronics toindependently interrogate the patient's skin.
 4. An apparatus as recitedin claim 3: wherein each of the sensors is configured to measure anequivalent sub-epidermal capacitance of a target region of skin; saidsub-epidermal capacitance corresponding to the moisture content of thetarget region of skin.
 5. An apparatus as recited in claim 4: whereinthe array of sensors comprises a first sensor having a first contactarea and a second sensor having a second contact area larger than thefirst sensor; and wherein the first and second sensors interrogate theskin at different depths.
 6. An apparatus as recited in claim 4: whereinthe substrate comprises a substrate assembly comprising a substratelayer; and wherein the sensor comprises a sensing pad having a firstelectrode embedded on a first side of the substrate and a secondelectrode embedded on a second side of the substrate.
 7. An apparatus asrecited in claim 6, further comprising a biocompatible cover layerdisposed over said first side of said substrate layer.
 8. An apparatusas recited in claim 6, further comprising a cover layer disposed undersaid second side of said substrate layer.
 9. An apparatus as recited inclaim 6, further comprising: a stiffener layer disposed under saidsecond side of said substrate layer; wherein the stiffener layercomprises a footprint substantially similar to that of the sensor array.10. An apparatus as recited in claim 6: wherein said first electrodecomprises an annular ring having an inner radius and an outer radius;wherein said second electrode comprises an outer radius having a smallerdiameter than the inner radius of the first electrode; and wherein saidsecond electrode is concentric with said first radius.
 11. An apparatusas recited in claim 1, wherein the interface electronics are configuredto transmit data retrieved from said sensors.
 12. An apparatus asrecited in claim 4, further comprising: a pressure sensor positioned inline with said RF sensor; said pressure sensor configured to measure anapplied pressure of the substrate at a location on the patient's skin.13. An apparatus as recited in claim 1, wherein the flexible substratecomprises Kapton or Polyimide.
 14. A scanner for sensing sub-epidermalmoisture from a location external to a patient's skin, comprising: anarray of bipolar RF sensors embedded on a flexible substrate; and aconformal pressure pad disposed adjacent and underneath the substrate;wherein the conformal pressure pad is configured to support the flexiblesubstrate while allowing the flexible substrate to conform to anon-planar sensing surface of the patient's skin; wherein said sensorarray is configured to emit and receive RF energy to interrogate thepatient's skin; and wherein each of the sensors are independently areindividually wired to independently interrogate the patient's skin. 15.A scanner as recited in claim 14, further comprising: interfaceelectronics coupled to the sensor; wherein said interface electronics isconfigured to control the emission and reception of RF energy.
 16. Ascanner as recited in claim 14, further comprising: an annular spaceradjacent and underneath the conformal pressure pad; wherein the annularspacer comprises a central opening configured to allow the conformalpressure pad to deflect freely into the central opening.
 17. A scanneras recited in claim 14: wherein each of the sensors is configured tomeasure an equivalent sub-epidermal capacitance of a target region ofskin; said sub-epidermal capacitance corresponding to the moisturecontent of the target region of skin.
 18. A scanner as recited in claim14: wherein the array of sensors comprises a first sensor having a firstcontact area and a second sensor having a second contact area largerthan the first sensor; and wherein the first and second sensorsinterrogate the skin at different depths.
 19. A scanner as recited inclaim 14: wherein each sensor comprises a first electrode in the form ofan annular ring having an inner radius and an outer radius and a secondelectrode comprising an outer radius having a smaller diameter than thefirst electrode; and wherein said second electrode is concentric withsaid first radius.
 20. A scanner as recited in claim 19: wherein thesubstrate comprises a substrate assembly comprising a substrate layer;and wherein the first electrode is embedded on a first side of thesubstrate and the second electrode embedded on a second side of thesubstrate.
 21. A scanner as recited in claim 20, further comprising: anupper biocompatible cover layer disposed over said first side of saidsubstrate layer and a lower cover layer disposed under said second sideof said substrate layer.
 22. A scanner as recited in claim 20, furthercomprising: a stiffener layer disposed under said second side of saidsubstrate layer; wherein the stiffener layer comprises a footprintsubstantially similar to that of the sensor array.
 23. A scanner asrecited in claim 14, further comprising: an array of pressure sensorspositioned in line with said RF sensor; said pressure sensors areconfigured to measure an applied pressure of the substrate atcorresponding locations on the patient's skin.
 24. A method formonitoring the formation of pressure ulcers at a target location of apatient's skin, comprising: positioning a flexible substrate adjacentthe target location of the patient's skin; the flexible substratecomprising one or more bipolar RF sensors; conforming the flexiblesubstrate to the patient's skin at the target location; exciting the oneor more bipolar RF sensors to emit RF energy into the patient's skin;and measuring the capacitance of the skin at the target location as anindicator of the Sub-Epidermal Moisture (SEM) at the target location.25. A method as recited in claim 24: wherein the one or more sensorscomprise an array of sensors disposed across said substrate; and whereinthe one or more sensors are individually controlled to independentlyexcite the one or more sensors.
 26. A method as recited in claim 24,further comprising: measuring an applied pressure of the substrate atthe target location on the patient's skin.
 27. A method as recited inclaim 25, further comprising: measuring an applied pressure of thesubstrate on the patient's skin at each of the sensors in the array.